Problem: $\dfrac{9}{4} - \dfrac{3}{10} = {?}$
Explanation: $ = {\dfrac{9 \times 5}{4 \times 5}} - {\dfrac{3 \times 2}{10 \times 2}} $ $ = {\dfrac{45}{20}} - {\dfrac{6}{20}} $ $ = \dfrac{{45} - {6}}{20} $ $ = \dfrac{39}{20}$